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Roles of the Eph Family Receptor Ephb1 and Ligand Ephrin-B2

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Roles of the Eph Family Receptor Ephb1 and Ligand Ephrin-B2 The Journal of Neuroscience, March 15, 1999, 19(6):2090–2101 Specification of Distinct Dopaminergic Neural Pathways: Roles of the Eph Family Receptor EphB1 and Ligand Ephrin-B2 Yong Yue,1 David A. J. Widmer,2 Alycia K. Halladay,2 Douglas Pat Cerretti,3 George C. Wagner,2 Jean-Luc Dreyer,4 and Renping Zhou1 1Laboratory for Cancer Research, College of Pharmacy, and 2Department of Psychology, Rutgers University, Piscataway, New Jersey 08855, 3Immunex Corporation, Seattle, Washington 98101, and 4Department of Biochemistry, University of Fribourg, 1700 Fribourg, Switzerland Dopaminergic neurons in the substantia nigra and ventral teg- cell loss of substantia nigra, but not ventral tegmental, dopa- mental area project to the caudate putamen and nucleus minergic neurons. These studies suggest that the ligand–recep- accumbens/olfactory tubercle, respectively, constituting meso- tor pair may contribute to the establishment of distinct neural striatal and mesolimbic pathways. The molecular signals that pathways by selectively inhibiting the neurite outgrowth and confer target specificity of different dopaminergic neurons are cell survival of mistargeted neurons. In addition, we show that not known. We now report that EphB1 and ephrin-B2, a recep- ephrin-B2 expression is upregulated by cocaine and amphet- tor and ligand of the Eph family, are candidate guidance mol- amine in adult mice, suggesting that ephrin-B2/EphB1 interac- ecules for the development of these distinct pathways. EphB1 tion may play a role in drug-induced plasticity in adults as well. and ephrin-B2 are expressed in complementary patterns in the midbrain dopaminergic neurons and their targets, and the li- Key words: axonal guidance; dopaminergic pathways; Eph gand specifically inhibits the growth of neurites and induces the family receptors; ephrins; drug addiction; plasticity The midbrain dopaminergic neurons are located primarily in two receptors (Zhou, 1998). This family is unique among tyrosine adjacent regions, the more lateral substantia nigra and the more kinase receptors in that all of the ligands are membrane-anchored medial ventral tegmental area, and project to the forebrain, form- and in that the association is required for activity (Davis et al., ing several distinct pathways (Ungerstedt, 1971; Moore and 1994). The soluble ligands lack biological activity and can func- Bloom, 1978; Lindvall and Bjorklund, 1983; Di Chiara et al., tion as antagonists (Gao et al., 1996). The requirement of mem- 1992; Heimer et al., 1995). Ventral tegmental dopaminergic neu- brane anchorage makes the Eph family ligands uniquely qualified rons send their axons to the ventromedial striatum (which in- as local guidance cues for axonal targeting. cludes nucleus accumbens and olfactory tubercle), constituting In vivo and in vitro observations indicate that the Eph family the mesolimbic pathway, and to the cortex (mesocortical pathway) ligands and receptors play key roles in the specification of topo- (Simon et al., 1976, 1979; Nauta et al., 1978; Beckstead et al., graphic projections. In the retinotectal and hippocamposeptal 1979). In contrast, substantia nigra dopaminergic neurons selec- systems, Eph family ligands and receptors are expressed in pro- tively project to dorsolateral striatum (caudate putamen) in an jecting and target fields in opposing gradients (Cheng et al., 1995; orderly medial-to-lateral arrangement, forming the nigrostriatal Drescher et al., 1995; Gao et al., 1996; Zhang et al., 1996). pathway (Carter and Fibiger, 1977; Fallon et al., 1978; Nauta et Consistent with the expression patterns, ligand–receptor interac- al., 1978; Beckstead et al., 1979; van der Kooy, 1979). Although tions repel and/or inhibit the growth of receptor-positive axons, these pathways have been identified for nearly three decades, the thus contributing to the specification of topographic projection underlying molecular mechanisms for the development of these maps (Drescher et al., 1995; Gao et al., 1996, 1998; Nakamoto et distinct pathways are still unknown. al., 1996). The Eph family receptor tyrosine kinases and their ligands To examine the roles of the Eph family ligands and receptors in have been implicated in guiding axons during the development of the development of the ascending midbrain dopaminergic path- the nervous system (for review, see Harris and Holt, 1995; ways, we investigated the developmental expression of these guid- Tessier-Lavigne, 1995; Friedman and O’Leary, 1996; Orioli and ance molecules in the dopaminergic neurons and their projection Klein, 1997; Pasquale, 1997; Flanagan and Vanderhaeghen, 1998; targets, including the caudate putamen, nucleus accumbens, and Zhou, 1998). The Eph family is the largest known group of olfactory tubercle. We further examined the biological effects of receptor tyrosine kinases, including at least eight ligands and 14 the Eph ligands on dopaminergic neurons and their regulation by cocaine and amphetamine in vivo. Our studies indicate that the Received July 16, 1998; revised Nov. 23, 1998; accepted Dec. 22, 1998. Eph family receptors and ligands may play important roles in This research was funded by the National Institute on Drug Abuse (Grant regulating the formation of distinct dopaminergic pathways and 1RO1DA11480-01) and by an Exploratory Research grant from the National Insti- may contribute to drug-induced neural plasticity. tute of Environmental and Occupational Health Sciences. We thank W. Schultz for the critical reading of this manuscript. MATERIALS AND METHODS Correspondence should be addressed to Dr. Renping Zhou, Laboratory for Cancer Research, Department of Chemical Biology, College of Pharmacy, Rutgers Animals and preparation of tissue sections. CD-1 mice from embryonic day University, Piscataway, NJ 08855. (E) 14 to postnatal day (P) 60 (adult) were used in in situ hybridization Copyright © 1999 Society for Neuroscience 0270-6474/99/192090-12$05.00/0 experiments. The day of vaginal plug occurrence was defined as E1 and Yueetal.• Specification of Dopaminergic Pathways by Ephrins J. Neurosci., March 15, 1999, 19(6):2090–2101 2091 Table 1. Expression of Eph family receptors in the P7 midbrain dopamine neurons Eph receptor Midbrain region EphA3 EphA4 EphA5 EphA6 EphA7 EphA8 EphB1 EphB2 EphB3 SN 2 2 11 2 2 2 111 2 2 VTA 2211222622 2, Expression below detection; 6, low expression; 11, moderate expression; 111, strong expression. the day of birth as P1. At least three animals were investigated at each staining with polyclonal anti-ephrin-B2 antibody (Santa Cruz, CA). Pos- age group. Whole embryos and brains of postnatal mice were dissected itive stainings were found in the ephrin-B2-transfected cells. In contrast, under carbon dioxide anesthesia and frozen on dry ice. Coronal and no significant staining was observed in parental or vector-transfected sagittal sections of 16 mm thickness were cut on a cryostat at 223°C and NIH-3T3 cells. mounted on slides coated with 2% triethoxy-3-aminopropyl saline (Sig- Neuron culture and staining. The substantia nigra and ventral tegmental 2 ma, St. Louis, MO). Then the slides were stored at 80°C before use. area of E18 rat embryos were dissected from the lateral two-thirds and 35 In situ hybridization. mRNA expression was detected with either [ S]- the medial one-third of the ventral mesencephalon, respectively, under a labeled in vitro transcribed riboprobes or end-labeled oligonucleotide microscope in PBS. The precise positions of substantia nigra and ventral probes. In situ hybridization was performed as described (Zhang et al., tegmental area were determined by tyrosine hydroxylase (TH) immuno- 1997). The optimal exposure time of hybridized sections to autoradio- histochemical staining of E18 rat midbrain sections. Neurons then were graphic emulsion was determined by exposing the sections to x-ray film dissociated and cocultured with monolayer control NIH-3T3 cells or for various time periods before dipping. For quantitative in situ hybrid- ephrin-B2-expressing fibroblasts in DMEM supplemented with fetal ization, complete sets of brain sections from different age or treatment m groups were analyzed in the same experiment with the same probe. bovine serum (10%), penicillin (50 U/ml), and streptomycin (50 g/ml). Different samples were compared only within the same experiment. Neurons were cultured for various times and stained with a monoclonal Developmental expression of nine Eph family tyrosine kinase recep- anti-TH antibody (Chemicon, Temecula, CA). The number of neurons tors was investigated via in situ hybridization. Only EphB1 showed and the lengths of neurites were measured with a Zeiss Telaval 31 specific differential expression in the midbrain dopaminergic neurons. microscope (Oberkochen, Germany). For quantitation of each sample, 20 EphB1 mRNA was detected with a riboprobe transcribed in vitro from a random fields were chosen from top to bottom and from the left to right 2.4 kb mouse EphB1 cDNA containing most of the coding region cloned sides of culture wells to represent the entire culture. in a pBluescript SK plasmid. Antisense riboprobe was synthesized with Drug treatment. From 30 to 180 mg/kg body weight of cocaine or T7 RNA polymerase for hybridization, and a sense control probe was D-amphetamine was injected subcutaneously in the neck of mice in four generated with T3 RNA polymerase. The synthesized riboprobes were divided doses over 6 hr. The mice were killed 6 hr or 1, 4, 7, or 14 d after hydrolyzed to smaller fragments (;0.2 kb) by 0.2 M bicarbonate at 60°C treatment, and the expression of ephrin-B2 in the striatum was analyzed for 41.6 min before hybridization. with in situ hybridization. To examine the expression of the ligands of EphB1, we performed in situ hybridization analyses with probes of all three ephrin-B ligands. Only ephrin-B2 showed differential expression in the dopaminergic target RESULTS fields. Ephrin-B2 mRNA was detected with a riboprobe made froma1kb human ephrin-B2 cDNA containing the full coding region in pBluescript Expression of Eph family receptor EphB1 in the 2 SK . Human ephrin-B2 has a 93% homology with mouse ephrin-B2 in midbrain dopaminergic neurons the nucleotide level (Bergemann et al., 1995; Cerretti et al., 1995).
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